Coal is the most abundant fossil fuel currently available. Most of the electricity generated in the world uses coal as the fuel. Oxygen (O2) enrichment during the combustion process improves combustion characteristics, both in terms of efficiency and pollutant emission levels. O2 enrichment in the fuel-rich ignition zone increases the local temperature. Increasing the temperature in the fuel-rich ignition zone allows a quicker and more efficient release of volatiles contained in the pulverized fuel, thus increasing the flame stability, enhancing the combustion efficiency, enabling an easier operation and saving fuel. Increasing the temperature in the fuel-rich ignition zone also decreases the pollutant emissions, especially nitrogen oxide (or dioxide, etc., hereinafter NOx) formation, since fuel-rich combustion coupled with high temperatures prevents fuel-bound nitrogen from being oxidized to NOx, by reducing it to molecular nitrogen N2.
The enrichment of a particle-laden stream, such as a coal/air stream, with O2 poses challenges. Due to safety concerns, it is desirable to limit the O2 concentration near walls of carbon steel ducts or pipes. O2 injection may also disturb coal particle trajectories leading to a non-uniform loading of the particles in the stream. This could lead to pockets that are fuel lean. This, in turn, has a detrimental effect on the NOx emissions, which tend to increase under such conditions.
In addition to reducing NOx emissions, carbon dioxide (CO2) emissions, not traditionally considered as a pollutant, have recently moved to the forefront of concern due to their contribution to global warming.
Therefore, there exists a need in the art for other processes of generating electricity, particularly processes that are more environmentally friendly.